Metered dose inhalers are known which deliver a measured amount of a therapeutic drug for treating patients with respiratory ailments. Optimum application occurs when the patient inhales a mist of the medicating drug into lung bronchia and bronchiole. The patient is instructed to place his lips around the mouthpiece of the inhaler and release a charge of medicament into his mouth. However, the medicament is pressurized in the inhalers and is discharged in a high velocity stream that impacts the patient's oropharynx rather than developing a mist that the patient can inhale into his lungs. Unfortunately, the sensation derived from the stream impacting the oropharynx may erroneously convince the patient that the required amount of medicament has been inhaled. As a result, the respiratory ailment remains relatively untreated. In addition, the impact of some drugs on throat tissue can cause undesirable side effects.
Current inhalation techniques teach that a slow, deep inhale is needed to maximize the amount of medicament deposited to a patient's bronchia and bronchiole. However, a patient suffering from a respiratory ailment such as asthma generally suffers from a reduced inhalation capacity--he has great difficulty in taking a slow breath and generally cannot take a deep breath. The breathing technique of the asthmatic patient better approximates a pant of several quick and shallow breaths. Hence, the need exists for a device which allows a respiratory patient to inhale the prescribed medicament during one of these short breaths.
Patients with severe asthma or chronic bronchitis are often instructed to apply their inhaler medication 2 to 5 times daily. Because the medication must be uncontaminated, the inhaler and any inhaler accessory devices must be clean. This requires either disposable devices or ability to clean the devices if they are to be reused.
It is known in the art to have chambers that receive discharge from an inhaler of pressurized medicament from which the patient inhales his medication. Nowacki, U.S. Pat. No. 4,470,412, discloses an inhalation valve in an expansion chamber for simplifying patient inhalation and improving mist formation. The inhalation valve includes a flexible diaphragm member and a support structure positioned upstream of the diaphragm thereby preventing backflow of fluid. The chamber also includes vent holes which allow ambient air into the chamber. Similarly, Hansen, U.S. Pat. No. 3,897,779, teaches a metered dose inhaler with a chamber having vent holes located near the upstream end o fan expansion chamber. Also, McCarty, U.S. Pat. No. 4,953,545, discloses a tapered chamber in combination with a mouthpiece offset from its chamber longitudinal axis to promote swirling within the chamber thereby causing large droplets to precipitate out of the mist before inhalation by the patient. None of these disclosures describe an easily cleaned, reusable expansion chamber in which a medicament mist can be formed and withdrawn by an asthmatic user in a short, quick breath.
It is therefore an object of this invention to provide a substantially sealed, constant-volume expansion chamber with unrestricted fluid flow therethrough for use in combination with a metered-dosage inhaler for delivering a medicament mist to a user's lungs. A further object is that dimensional parameters of the chamber be optimized to maximize the concentration of the medicament mist in the chamber. Another object is to provide an expansion chamber that allows the medicament mist to be substantially withdrawn during a single short breath characteristic of asthmatic users. A final object is that the expansion chamber be reusable and thus can be easily cleaned.